Cyto-histo correlations of plasmacytoid and micropapillary variants of high-grade urothelial carcinoma: do they fit well in The Paris System for reporting urinary cytology?

Introduction: Plasmacytoid and micropapillary variants of high-grade urothelial carcinoma (HGUC) exhibit unique histologic morphology and very aggressive clinical behavior. However, the morphology of these 2 variants in urinary cytology is not well studied and evaluated using The Paris System for reporting urinary cytology. Materials and methods: A database search was performed in all patients with the diagnosis of plasmacytoid or micropapillary HGUC. A total of 5 patients with positive urinary cytology cases were identified. The cytomorphology of every urinary cytology case was correlated with the histologic features in the surgical specimens from the same patient. Results: One urine and 4 bladder washings were evaluated. Cytologically, plasmacytoid HGUCs are characterized by single, large tumor cells with hyperchromasia, irregular nuclear membranes, and vacuolated cytoplasm. The nuclear-to-cytoplasmic (N:C) ratio was less than 0.5 in many of the malignant cells due to the abundant cytoplasm. The cytology features of micropapillary HGUC include the presence of micropapillae of tumor cells with no fibrovascular core. Individual high-grade urothelial cells were also identified in all 4 cases, but 1 (25%) of these had only rare cells meeting The Paris System criteria for HGUC due to abundant cytoplasm and lack of hyperchromasia in most malignant cells. Conclusions: Plasmacytoid and micropapillary variants of HGUC have unique cytomorphologic features in urinary cytology specimens, which are reflective of the corresponding histological findings. These 2 clinically aggressive variants of HGUC may not be as readily interpreted as malignant using The Paris System for reporting urinary cytology, creating potential diagnostic pitfalls.